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Huang, Z., Tu, Y., Meng, S., Sabau, C., Popescu, C. & Sas, G. (2019). Experimental study on shear deformation of reinforced concrete beams using digital image correlation. Engineering structures, 181, 670-698
Open this publication in new window or tab >>Experimental study on shear deformation of reinforced concrete beams using digital image correlation
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2019 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 181, p. 670-698Article in journal (Refereed) Published
Abstract [en]

This paper presents an experimental program aimed at providing reliable and comprehensive experimental data for assessing the available models of predicting the shear deformation of diagonally-cracked reinforced concrete (RC) beams. The non-contact measuring technique, Digital Image Correlation (DIC), was used to monitor the full-field displacement and strain in the shear span of five RC beams with thin webs. Virtual measuring grids were created to measure the mean shear strain and other critical deformation results which reflects the mechanism of shear deformation after shear cracking (i.e. the principal compressive strain angle, the principal compressive strain, the mid-depth longitudinal strain and the mean vertical strain). The experimental mean shear strain and other critical deformation results were compared with the predictions with several available models. The comparison indicates the available models fail to reproduce the principal compressive strain angle, the mid-depth longitudinal strain and the mean vertical strain which constitute the key parameters in estimating the shear deformation after shear cracking. As a result, significant discrepancies in the shear deformation of the beams tested in this paper are observed between the experimental and calculated results. It is also found that the predicted shear deformation of a number of beam specimens tested by other researchers with the available models deviates considerably from the experimental results. In general, the existing models are not capable of providing accurate predictions of the shear deformation of RC beams and further investigation into this topic is needed.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Reinforced concrete beams, Shear deformation, Experimental study, Digital image correlation
National Category
Other Materials Engineering
Research subject
Building Materials
Identifiers
urn:nbn:se:ltu:diva-72817 (URN)10.1016/j.engstruct.2018.12.056 (DOI)000456754400049 ()2-s2.0-85058962784 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-02-07 (johcin)

Available from: 2019-02-07 Created: 2019-02-07 Last updated: 2019-02-22Bibliographically approved
Sabau, C., Popescu, C., Bagge, N., Sas, G., Blanksvärd, T. & Täljsten, B. (2019). Local and global behavior of walls with cut-out openings in multi-story reinforced concrete buildings. Engineering structures, 187, 57-72
Open this publication in new window or tab >>Local and global behavior of walls with cut-out openings in multi-story reinforced concrete buildings
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2019 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 187, p. 57-72Article in journal (Refereed) Published
Abstract [en]

This paper presents the finite element analysis (FEA) results of a multi-story reinforced concrete (RC) building having precast and cast-in-place load bearing walls. Door-type cut-out openings (height: 2.1 m, width: 0.9–4.4 m) were created at the first and second story of the building. Results from experimental tests on axially loaded RC panels were used to verify the modeling approach. The influence of cut-out openings on the response of individual RC panels, failure modes, and load redistribution to adjacent members was analyzed. Moreover, the wall bearing capacities obtained from FEA were compared with the values calculated from design equations. The results revealed that the robustness of multi-story buildings having RC load bearing wall systems decrease considerably with the creation of cut-out openings. However, owing to the initial robustness of the buildings, large cut-outopenings could be created under normal service conditions without strengthening of the building structure. Furthermore, design equations provided very conservative predictions of the ultimate capacity characterizing the solid walls and walls with small openings, whereas similar FEA and analytically predicted capacities were obtained for walls with large openings.

Keywords
FEM, reinforced concrete, building assessment, wall, openings
National Category
Building Technologies Other Civil Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-70883 (URN)10.1016/j.engstruct.2019.02.046 (DOI)2-s2.0-85062088838 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-03-07 (inah)

Available from: 2018-09-18 Created: 2018-09-18 Last updated: 2019-03-07Bibliographically approved
Nilimaa, J., Sabau, C., Bagge, N., Puurula, A., Sas, G., Blanksvärd, T., . . . Elfgren, L. (2018). Assessment and Loading to Failure of Three Swedish RC Bridges. In: Eva Lantsoght and Pinar Okumus (Ed.), Evaluation of Concrete Bridge Behavior through Load Testing: International Perspectives (pp. 8.1-8.18). Faarmington Hills, MI: American Concrete Institute, 323, Article ID SP-323-8.
Open this publication in new window or tab >>Assessment and Loading to Failure of Three Swedish RC Bridges
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2018 (English)In: Evaluation of Concrete Bridge Behavior through Load Testing: International Perspectives / [ed] Eva Lantsoght and Pinar Okumus, Faarmington Hills, MI: American Concrete Institute, 2018, Vol. 323, p. 8.1-8.18, article id SP-323-8Chapter in book (Refereed)
Abstract [en]

Current codes often underestimate the capacity of existing bridges. The purpose of the tests presented here has been to assess the real behaviour and capacity of three types of bridges in order to be able to utilize them in a more efficient way.

The three studied bridges are: (1) Lautajokk – A one-span trough bridge tested in fatigue to check the shear capacity of the section between the slab and the girders; (2) Övik – A two span trough bridge strengthened with Near Surface Mounted Reinforcement (NSMR) of Carbon Fibre Reinforced Polymers (CFRP) tested in bending, shear and torsion; and (3) Kiruna – A five-span prestressed three girder bridge tested to shear-bending failures in the girders and in the slab.

The failure capacities were considerably higher than what the code methods indicated. With calibrated and stepwise refined finite element models, it was possible to capture the real behaviour of the bridges. The experiences and methods may be useful in assessment and better use of other bridges.

Place, publisher, year, edition, pages
Faarmington Hills, MI: American Concrete Institute, 2018
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-69992 (URN)978-1-64195-007-7 (ISBN)
Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-08-10Bibliographically approved
Sabau, C., Popescu, C., Sas, G., Blanksvärd, T. & Täljsten, B. (2018). Axially Loaded RC Walls with Cutout Openings Strengthened with FRCM Composites. Journal of composites for construction, 22(6), 04018046-1-04018046-16, Article ID 04018046.
Open this publication in new window or tab >>Axially Loaded RC Walls with Cutout Openings Strengthened with FRCM Composites
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2018 (English)In: Journal of composites for construction, ISSN 1090-0268, E-ISSN 1943-5614, Vol. 22, no 6, p. 04018046-1-04018046-16, article id 04018046Article in journal (Refereed) Published
Abstract [en]

Upgrading existing buildings to new functional requirements may require new openings that can weaken the structure, promptingthe need for strengthening. In such cases traditional strengthening solutions, such as creating a reinforced concrete (RC) or steel frame aroundthe opening, imply long-term restrictions in the use of the structure compared to solutions that use externally bonded composites. Two fabricreinforcedcementitious matrix (FRCM) composites were used in this study to restore the capacity of panels with newly created doortype openings to that of a solid panel. Five half-scale RC panels acting as two-way action compression members were tested to failure.Two full-field optical deformation measurement systems were used to monitor and analyze the global structural response of each testedpanel (i.e., crack pattern, failure mechanism, and displacement/strain fields). The performance of existing design methods for RC panelshas been assessed in comparison with the experimental results. The capacity of strengthened panels with small openings (450 × 1,050 mm) was entirely restored to that of the solid panel. However, for panels with large openings (900 × 1,050 mm), only 75% of the solid panel’scapacity was restored. The capacity of the strengthened panels was about 175 and 150% higher compared to that of reference panels withsmall and large openings, respectively.

Place, publisher, year, edition, pages
American Society of Civil Engineers (ASCE), 2018
Keywords
FRCM, Reinforced concrete, Walls with openings, Digital image correlation
National Category
Infrastructure Engineering Building Technologies
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-70579 (URN)10.1061/(ASCE)CC.1943-5614.0000867 (DOI)000447252600001 ()2-s2.0-85051927413 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-24 (andbra)

Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-10-29Bibliographically approved
Täljsten, B., Blanksvärd, T., Sas, G., Bagge, N., Nilimaa, J., Popescu, C., . . . Häggström, J. (2018). Bridges tested to failure in Sweden. In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark: . Paper presented at IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark.
Open this publication in new window or tab >>Bridges tested to failure in Sweden
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2018 (English)In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark, 2018Conference paper, Published paper (Refereed)
Abstract [en]

Five bridges of different types have been tested to failure and the results have been compared to analyses of the load-carrying capacity using standard code models and advanced numerical methods. The results may help to make accurate assessments of similar existing bridges. There it is necessary to know the real behaviour, weak points, and to be able to model the load-carrying capacity in a correct way.The five bridges were: (1) a strengthened one span concrete road bridge - Stora Höga ; (2) a one span concrete rail trough bridge loaded in fatigue – Lautajokk; (3) a two span strengthened concrete trough railway bridge - Övik; (4) a one span railway steel truss bridge -Åby; and (5) a five span prestressed concrete road bridge - Kiruna. The unique results in the paper are the experiences of the real failure types, the robustness/weakness of the bridges, and the accuracy and shortcomings/potentials of different codes and models for safety assessment of existing structures

Keywords
Test to failure, bridges of concrete and steel, Assessment, Strengthening, Monitoring, Bending, Shar, Torsion, Bond, Fatigue, Carbon Fibre Reinforced Polymers (CFRP)
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-72378 (URN)
Conference
IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2018-12-28
Huang, Z., Lu, Z., Song, S., Tu, Y., Blanksvärd, T., Sas, G. & Elfgren, L. (2018). Finite element analysis of shear deformation in reinforced concrete shear-critical beams. Structure and Infrastructure Engineering, 14(6), 791-806
Open this publication in new window or tab >>Finite element analysis of shear deformation in reinforced concrete shear-critical beams
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2018 (English)In: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 14, no 6, p. 791-806Article in journal (Refereed) Published
Abstract [en]

The objective of this paper was to study the contribution of shear deformation in reinforced concrete (RC) shear-critical beams. A 2D concrete material model based on smeared fixed crack was presented and incorporated into a commercial finite element (FE) software. A method of calculating shear and flexure deformation separately out of total deformation in the shear span was presented and implemented into the FE analysis. Several experiments of RC shear-critical beams were simulated and good agreement between the experimental and numerical results was obtained in terms of total deformation, flexure deformation, shear deformation and crack patterns. The results show that after shear cracking, the contribution of shear deformation to total deformation increases rapidly. The shear span-to-depth ratio, the longitudinal reinforcement, the shear reinforcement and the load level could be the critical factor to influence the contribution of shear deformation. It appears that for RC shear-critical beams without shear reinforcement, the deformational behaviour is governed by flexure deformation. However, for RC beams with shear reinforcement, the contribution of shear deformation is not negligible after shear cracks develop. Moreover, the measuring method could also affect the measured shear deformation. Finally, future work on experimental investigation into this topic is recommended.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-65169 (URN)10.1080/15732479.2017.1360915 (DOI)000429038000009 ()
Note

Validerad;2018;Nivå 2;2018-04-10 (andbra)

Available from: 2017-08-17 Created: 2017-08-17 Last updated: 2018-04-19Bibliographically approved
Duvnjak, I., Bartolak, M., Nilimaa, J., Sas, G., Blanksvärd, T., Täljsten, B. & Elfgren, L. (2018). Lessons Learnt from Full-Scale Tests of Bridges in Croatia and Sweden. In: IABSE Symposium, Nantes 2018: Tomorrow's Megastructures. Paper presented at 40th IABSE Symposium, 19-21 September 2018, Nantes, France.. International Association for Bridge and Structural Engineering, Article ID S23-127.
Open this publication in new window or tab >>Lessons Learnt from Full-Scale Tests of Bridges in Croatia and Sweden
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2018 (English)In: IABSE Symposium, Nantes 2018: Tomorrow's Megastructures, International Association for Bridge and Structural Engineering , 2018, article id S23-127Conference paper, Published paper (Refereed)
Abstract [en]

Load testing is a way to control the capacity and function of a bridge. Methods and recommendations for load testing are described and examples are given form tests carried out in Croatia and Sweden. In order not to damage the bridge being tested, the load must be limited, often to be within the serviceability limit state (SLS). Numerical models can be calibrated by load tests and then be used to check the carrying capacity for higher loads than what has been tested. Need for further work and recommendations are discussed. By effective planning, costs can be saved and a more sustainable use of bridges can be obtained.

Place, publisher, year, edition, pages
International Association for Bridge and Structural Engineering, 2018
Keywords
Load testing, proof loading, collapse, deformations, serviceability limit state (SLS), numerical modelling, stiffness
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-72381 (URN)2-s2.0-85059365622 (Scopus ID)9783857481611 (ISBN)
Conference
40th IABSE Symposium, 19-21 September 2018, Nantes, France.
Funder
EU, Horizon 2020
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2019-01-14Bibliographically approved
Coric, I., Täljsten, B., Blanksvärd, T., Sas, G., Ohlsson, U. & Elfgren, L. (2018). Railway Bridges on the Iron Ore Line in Northern Sweden– From Axle Loads of 14 to 32,5 ton. In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark: IABSE Reports, Vol 111. Paper presented at IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark. , 111
Open this publication in new window or tab >>Railway Bridges on the Iron Ore Line in Northern Sweden– From Axle Loads of 14 to 32,5 ton
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2018 (English)In: IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the FutureJune 25-27 2018, Copenhagen, Denmark: IABSE Reports, Vol 111, 2018, Vol. 111Conference paper, Published paper (Refereed)
Abstract [en]

The Iron Ore Railway Line was built around 1900 and has more than 100 bridges. It has a length of ca 500 km and runs from Kiruna and Malmberget in northern Sweden to the ice-free harbour in Narvik in Norway on the Atlantic and to Luleå in Sweden on the Baltic. The original axle load was 14 ton. The axle load has gradually been increased to 25 ton in 1955, to 30 ton in 1998 and to 32,5 ton in 2017.The increases in axle loads have been preceded by monitoring and assessment studies of the bridges. The capacity and need for strengthening or replacement of the bridges have been evaluated. Many of the bridges could carry a higher load than what it was designed for. Experiences from studies before the axle load was increased in 1998 and 2017 are presented and discussed.

Keywords
Railway bridges, foundations, steel, reinforced and prestressed concrete. Assessment, Strengthening, Fatigue
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-72379 (URN)
Conference
IABSE Conference 2018 – Engineering the Past, to Meet the Needs of the Future June 25-27 2018, Copenhagen, Denmark
Available from: 2018-12-28 Created: 2018-12-28 Last updated: 2018-12-28
Sabau, C., Popescu, C., Sas, G., Schmidt, J. W., Blanksvärd, T. & Täljsten, B. (2018). Strengthening of RC beams using bottom and side NSM reinforcement. Composites Part B: Engineering, 149, 82-91
Open this publication in new window or tab >>Strengthening of RC beams using bottom and side NSM reinforcement
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2018 (English)In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 149, p. 82-91Article in journal (Refereed) Published
Abstract [en]

The allowable strain in fibre reinforced polymers reinforcement is limited by design codes to avoid debonding. The near-surface mounted (NSM) reinforcement technique has been proven to produce better anchorage behaviour compared to externally bonded reinforcement solutions. However, NSM solutions do not always eliminate debonding issues, with concrete cover detachment (CCD) typically occurring in RC beams strengthened for flexure. This experimental study investigated the efficiency of side mounted (S) compared to bottom mounted (B) NSM bars to prevent CCD. The experimental results were compared to models available in the literature that predict the observed failure modes and the crack spacing in the NSM anchorage zone. Compared to B-NSM, the S-NSM solution was successful in avoiding brittle CCD failure and showed increased rotational capacity and energy dissipation at failure. Existing CCD debonding models were found to be conservative.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-68708 (URN)10.1016/j.compositesb.2018.05.011 (DOI)000442979500010 ()2-s2.0-85047119715 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-06-01 (svasva)

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2018-09-10Bibliographically approved
Popescu, C., Schmidt, J. W., Goltermann, P. & Sas, G. (2017). Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach (ed.). Engineering structures, 150, 585-598
Open this publication in new window or tab >>Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach
2017 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 150, p. 585-598Article in journal (Refereed) Published
Abstract [en]

Building refurbishment works frequently require the cutting of new openings in concrete walls. Cutting new openings weakens the overall response of such elements, so they usually require strengthening. However, current design codes offer little guidance on strengthening walls with openings, and less still on the use of non-metallic reinforcements such as FRP (Fibre Reinforced Polymers) to ensure sufficient load bearing capacity. This paper proposes a new procedure based on limit analysis theory for evaluating the ultimate load of walls with cut-out openings that have been strengthened with carbon-FRP (CFRP). First, the approach is verified against transverse (out-of-plane) and axial (in-plane) loading for unstrengthened specimens. These loading types result in different failure mechanisms: transverse loading leads to failure due to yielding/rupture of the steel reinforcement while axial loading leads to failure by concrete crushing. Second, the proposed method is further developed for CFRP-strengthened specimens under axial loading. It accounts for the contribution of CFRP indirectly, by updating the concrete model with an enhanced compressive strength as a result of confining the piers. Predictions made using the new method agree closely with experimental results.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-9022 (URN)10.1016/j.engstruct.2017.07.069 (DOI)000413125800044 ()2-s2.0-85026533028 (Scopus ID)794c01ea-1ee7-4cdf-8f59-1d088954f9bf (Local ID)794c01ea-1ee7-4cdf-8f59-1d088954f9bf (Archive number)794c01ea-1ee7-4cdf-8f59-1d088954f9bf (OAI)
Note

Validerad; 2017; Nivå 2; 2017-08-15 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8682-876x

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